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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

High spectral resolution measurement of gamma ray lines from the earth's atmosphere

A search for gamma ray line features from the earth's atmosphere has been conducted using data from the third High Energy Astronomy Observatory (HEAO 3) high spectral resolution gamma ray spectrometer. In addition to the strong line at 0.511 MeV, other intrinsically broadened line features have been observed at 1.63, 2.31, 3.67, 4.43, 5.09, and 6.13 MeV. Since the spectral resolution of the instrument is much finer than the width of the observed line features, the intrinsic width as well as the energy and intensity of each of these lines are reported. Several other predicted lines have also been observed. The characteristic of the lines seen by HEAO 3 are generally consistent with theoretical predictions as well as with previous measurements.

Willet, J. B.↗
NASA NTRS2008

Uncertainty Analysis of Air Radiation for Lunar Return Shock Layers

By leveraging a new uncertainty markup technique, two risk analysis methods are used to compute the uncertainty of lunar-return shock layer radiation predicted by the High temperature Aerothermodynamic Radiation Algorithm (HARA). The effects of epistemic uncertainty, or uncertainty due to a lack of knowledge, is considered for the following modeling parameters: atomic line oscillator strengths, atomic line Stark broadening widths, atomic photoionization cross sections, negative ion photodetachment cross sections, molecular bands oscillator strengths, and electron impact excitation rates. First, a simplified shock layer problem consisting of two constant-property equilibrium layers is considered. The results of this simplified problem show that the atomic nitrogen oscillator strengths and Stark broadening widths in both the vacuum ultraviolet and infrared spectral regions, along with the negative ion continuum, are the dominant uncertainty contributors. Next, three variable property stagnation-line shock layer cases are analyzed: a typical lunar return case and two Fire II cases. For the near-equilibrium lunar return and Fire 1643-second cases, the resulting uncertainties are very similar to the simplified case. Conversely, the relatively nonequilibrium 1636-second case shows significantly larger influence from electron impact excitation rates of both atoms and molecules. For all cases, the total uncertainty in radiative heat flux to the wall due to epistemic uncertainty in modeling parameters is 30% as opposed to the erroneously-small uncertainty levels (plus or minus 6%) found when treating model parameter uncertainties as aleatory (due to chance) instead of epistemic (due to lack of knowledge).

Kleb, Bil↗
NASA NTRS1977

Chromospheric limb spectra from Skylab - 2000 to 3200 A

Chromospheric limb spectra of a quiet-sun region between 2000 and 3200 A recorded by the normal-incidence spectrograph on Skylab are discussed. The spectral resolution is 0.12 A, and the projected slit area on the sun is 2 by 60 arcsec. A list of lines with wavelengths, identifications, and absolute intensities is given for the spectrum recorded at +4 arcsec outside the white-light limb. The intensity behavior outside the limb is shown for lines of the ions C II, Si II, Cr II, Mn II, Fe II, Fe III, Co II, and Ni II. The widths of the intersystem lines of Si II and C II increase monotonically with height above the limb. The full width at half-maximum of the Si II lines increases from 0.034 A at the limb to 0.27 A at +12 arcsec above the limb. The widths of the C II lines increase from 0.17 A at +2 arcsec to 0.31 A at +12 arcsec.

Doschek, G. A.↗
NASA NTRS1975

Forbidden Ca II in the sun unmasked by way of Venus

Eleven high dispersion spectra of Venus, taken with blue Doppler shifts, have been used to unmask the 7323.88 angstrom forbidden line of Ca II from the earth atmospheric H2O absorption line at 7323.972 angstroms. An equivalent width for the Ca II line has been obtained in integrated sunlight. A model giving the solar calcium abundance is presented.

Schorn, R. A.↗
NASA NTRS1984

Recalibration of Mount Wilson Doppler measurements (Research note)

The dispersion calibration of spectroscopic velocity measurements made with the 150-ft tower telescope at Mt. Wilson Observatory is revised upward by 0.55 percent on the basis of observations of the six lines of comparable shape and equivalent width nearest the 5250.2-A line of Fe-I used in the solar Doppler rate measurements. The dispersion results are presented in a graph, and the superiority of the Kitt Peak wavelength tables (Pierce and Breckenridge, 1973) over those of Moore et al. (1966) is demonstrated. As a result of the recalibration, all recent spectroscopic velocities from this telescope must be revised downward by 0.55 percent.

Snodgrass, H. B.↗
NASA NTRS1994

Highly ionized gas absorption in the disk and halo toward HD 167756 at 3.5 kilometers per second resolution

High-resolution spectra of interstellar Si IV, C IV, and N V absorption lines along the 4 kpc path to the inner Galaxy star HD 167756 at z = -0.85 kpc are presented. The spectra were obtained with the echelle mode of Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope (HST) and have signal-to-noise ratios ranging from 23 to 38. The high resolution of the measurements full width at half maximum (FWHM = 3.5 km/s) results in fully resolved line profiles for the highly ionized gas absorption. The measurements provide information on the column density per unit velocity, N(v), as a function of velocity for Si IV, C IV, and N V. The C IV and N V profiles extend from -70 to +70 km/s, while the Si IV profiles extend from -40 to +70 km/s. The integrated logarithmic column densities are long N(Si IV) = 13.09 +/- 0.02, log N(C IV) = 13.83 +/- 0.02, and log N(N V) = 13.56 +/- 0.03. The N V profile is broad, asymmetric, and featureless, while the Si IV profile contains narrow absorption components near V(sub LSR) = -19, 0, +20, and +52 km/s with Doppler spread parameters, b about = 10-12 km/s. The C IV profile contains both broad and narrow structure. The high ion feature near +52 km/s is also detected in the low-ionization lines of Ca II, O I, Si II, and Fe II. The other narrow Si IV and C IV components occur within several km/s of components seen in low-ionization species. The sight line contains at least two types of highly ionized gas. One type gives rise to a broad N V profile, and the other results in the more structured Si IV profile. The C IV profile contains contributions from both types of highly ionized gas. The broad but asymmetric N V profile is well represented by a large Galactic scale height gas which is participating in Galactic rotation and has a combination of thermal and turbulent broadening with b(sub tot) about = 42 km/s. The C IV to N V abundance ratio of 1.0 +/- 0.3 for the gas implies T about 1.6 x 10(exp 5) K or about 8 x 10(exp 5) K if the gas is in collisional ionization equilibrium and has a solar carbon to nitrogen abundance ratio. This absorption may be associated with cooling hot gas situated in Galactic shells and supershells along the sight line. The gas producing the narrow Si IV and C IV absorption components has line widths that are compatible with origins in conductive interfaces between the warm and hot interstellar medium. Kinematic flows associated with the photoionized edges of clouds might also produce Si IV and C IV lines with Doppler spread parameters similar to those observed, but the C IV to Si IV ratio in this gas is 3.5, which leads us to favor the conductive interface interpretation.

Savage, Blair D.↗
NASA NTRS1990

Atoms in carbon cages as a source of interstellar diffuse lines

A model to describe the resonance absorption lines of various atoms trapped in closed carbon cages is presented. These systems may be responsible for some of the as yet unexplained diffuse interstellar bands. Model potentials for possible atom-C60 systems are obtained and used to calculate the resonance lines. The trapped atoms considered are O, N, Si, Mg, Al, Na, and S, and in all cases the resonance lines are shifted toward the red as compared to the isolated atoms. The calculated wavelengths are compared to the range of wavelengths observed for the diffuse interstellar bands, and good agreement is found for Mg and Si resonance lines. Other lines may be caused by other than resonance transitions or by trapped molecules. The oscillator strengths and the abundances are evaluated and compared with observation. Mechanisms to explain the observed band width of the lines and the existence of certain correlated pairs of lines are discussed.

Ballester, J. L.↗
NASA NTRS1986

Velocity-resolved observations of water in Comet Halley

An infrared spectrum of comet Halley was recorded at the Kuiper Airborne Observatory with an instrumental velocity resolution of 1.1 km/sec. A total of 13 emission lines in the 2.65 micron spectral region were assigned to neutral gaseous H2O : 10 in the 001 to 000 band and 3 in the hot 011 to 010 band. The position and widths of these lines are functions of the gas velocity field in the coma. Analysis indicates that the neutral gas outflow is widely dispersed about the nucleus. This spectroscopic picture is consistent with spacecraft images that show multiple jets releasing material into most of the sunfacing hemisphere.

Larson, Harold P.↗
NASA NTRS1979

A possible line feature at 73 keV from the Crab Nebula

Evidence is reported for a possible line feature at 73 keV from the Crab Nebula. The experiment was conducted with a balloon-borne high-resolution gamma-ray spectrometer on June 10, 1974, over Palestine, Texas. The intensity and the width of the line derived from the fitting of these data are approximately 0.0038 photon per (sq cm-sec) and less than 4.9 keV FWHM, respectively. The line is superposed on a power-law continuum of 11.2 E to the -2.16 photons per (sq cm-keV) in the energy range from 53 to 300 keV, which is consistent with other measurements of the Crab Nebula spectrum.

Ling, J. C.↗
NASA NTRS1983

Theoretical quasar emission-line profiles. II - Effects of source function vibration and total thickness

By calculating the actual limb brightening functions for the emission-line clouds, rather than using the approximation that all observed radiation originates from the same part of the growth curve, the present consideration of radiation transfer effects in the broad emission line regions of quasars and Seyfert 1 galaxies allows the study of clouds whose total optical thickness is intermediate between the limiting cases of an optically thin Doppler core and Voigt wing emissions. The ability to predict minor differences in observed line profiles in a given object in terms of radiative transfer effects leads to the proposal of a test which may be able to distinguish between radial and orbital geometries. The test involves the difference in width between emission lines from the same family having different optical depth scales.

Puetter, R. C.↗
NASA NTRS2012

An Fe XXIV Absorption Line in the Persistent Spectrum of the Dipping Low-Mass X-Ray Binary 1A 1744-361

We report on Chandra X-ray Observatory (Chandra) High Energy Transmission Grating spectra of the dipping low-mass X-ray binary 1A 1744−361 during its 2008 July outburst. We find that its persistent emission is well modeled by a blackbody (kT approx. 1.0 keV) plus power law (Gamma approx. 1.7) with an absorption edge. In the residuals of the combined spectrum, we find a significant absorption line at 6.961 +/- 0.002 keV, consistent with the Fe xxvi (hydrogen-like Fe) 2-1 transition.We place an upper limit on the velocity of a redshifted flow of nu < 221 km/s. We find an equivalent width for the line of 27+2/−3 eV, from which we determine a column density of (7 +/- 1)×10(exp 17) /sq. cm via a curve-of-growth analysis. Using XSTAR simulations, we place a lower limit on the ionization parameter of >103.6 erg cm/s. We discuss what implications the feature has on the system and its geometry. We also present Rossi X-ray Timing Explorer data accumulated during this latest outburst and, via an updated color-color diagram, clearly show that 1A 1744−361 is an "atoll" source

stars↗
NASA NTRS2009

An Fe XXVI Absorption Line in the Persistent Spectrum of the Dipping Low Mass X-ray Binary 1A 1744-361

We report on Chandra X-ray Observatory (CXO) High-Energy Transmission Grating (HETG) spectra of the dipping Low Mass X-ray Binary (LMXB) 1A 1744-361 during its July 2008 outburst. We find that its persistent emission is well modeled by a blackbody (kT approx. 1.0 keV) plus power-law (Gamma approx. 1.7) with an absorption edge at 7.6 keV. In the residuals of the combined spectrum we find a significant absorption line at 6.961+/-0.002 keV, consistent with the Fe XXVI (hydrogen-like Fe) 2 - 1 transition. We place an upper limit on the velocity of a redshifted flow of v < 221 km/s. We find an equivalent width for the line of 27+2/-3 eV, from which we determine a column density of 7+/-1 x 10(exp 17)/sq cm via a curve-of-growth analysis. Using XSTAR simulations, we place a lower limit on the ionization parameter of > 10(exp 3.6) erg cm/s. The properties of this line are consistent with those observed in other dipping LMXBs. Using Rossi X-ray Timing Explorer (RXTE) data accumulated during this latest outburst we present an updated color-color diagram which clearly shows that IA 1744-361 is an "atoll" source. Finally, using additional dips found in the RXTE and CXO data we provide an updated orbital period estimate of 52+/-5 minutes.

Gavriil, Fotis P.↗
NASA NTRS1972

Intensity and half width measurements of the /00 2 - 00 0/ band of N2O.

Measurements of the intensities and half widths of the lines of the (00 2 - 00 0) band of N2O have been made with a spectral resolution better than 0.06/cm. The band intensity has been determined to be 1.29/sq cm per atm at 296 K. The half widths have been measured for both N2 and self broadening.

Margolis, J. S.↗
NASA NTRS1988

A search for SH(+) toward Zeta Ophiuchi

A search has been made toward Zeta Ophiuchi for interstellar absorption from the R11(0) line in the A 3Pi-X 3Sigma(-)(0-0) band of SH(+) at a wavelength of 3363.49 A in a new observational test of recent magnetohydrodynamical shock models. A low upper limit has been derived to the equivalent width of this line, 0.64 mA, and the implications of this result are discussed.

Millar, T. J.↗
NASA NTRS2001

Evolution of Iron K Alpha Line Emission in the Black Hole Candidate GX 339-4

GX 339-4 was regularly monitored with the Rossi X-Ray Timing Explorer during a period (in 1999) when its X-ray flux decreased significantly (from 4.26 x 10(exp -10) to 7.6 x 10(exp -12) ergs in the 3-20 keV band), as the source settled into the 'off state.' Our spectral analysis revealed the presence of a prominent iron K alpha line in the observed spectrum of the source for all observations. The line shows an interesting evolution: it is centered at approx. 6.4 keV when the measured flux is above 5 x 10(exp -1) ergs per sq cm/s but is shifted to approx. 6.7 keV at lower fluxes. The equivalent width of the line appears to increase significantly toward lower fluxes, although it is likely to be sensitive to calibration uncertainties. While the fluorescent emission of neutral or mildly ionized iron atoms in the accretion disk can perhaps account for the 6.4 keV line, as is often invoked for black hole candidates, it seems difficult to understand the 6.7 keV line with this mechanism because the disk should be less ionized at lower fluxes (unless its density changes drastically). On the other hand, the 6.7 keV line might be due to a recombination cascade of hydrogen- or helium-like iron ions in an optically thin, highly ionized plasma. We discuss the results in the context of proposed accretion models.

Feng, Y. X.↗
NASA NTRS2006

Comprehensive Analysis of RXTE Data from Cyg X-1. Spectral Index-Quasi-Periodic Oscillation Frequency-Luminosity Correlations

We present timing and spectral analysis of approx. 2.2 Ms of Rossi X-ray Time Explorer (RXTE) archival data from Cyg X-1. Using the generic Comptonization model we reveal that the spectrum of Cyg X-1 consists of three components: a thermal seed photon spectrum, a Comptonized part of the seed photon spectrum and the iron line. We find a strong correlation between 0.1-20 Hz frequencies of quasiperiodic oscillations (QPOs) and the spectral power-law index. Presence of two spectral phases (states) are clearly seen in the data when the spectral indices saturate at low and high values of QPO frequencies. This saturation effect was discovered earlier in a number of black hole candidate (BHC) sources and now we strongly confirm this phenomenon in Cyg X-1. In the soft state this index- QPO frequency correlation shows a saturation of the photon index Gamma approx. 2.1 at high values of the low frequency upsilon(sub L). The saturation level of Gamma approx. 2.1 is the lowest value found yet in BHCs. The bolometric luminosity does not show clear correlation with the index. We also show that Fe K(sub alpha) emission line strength (equivalent width, EW) correlates with the QPO frequency. EW increases from 200 eV in the low/hard state to 1.5 keV in the high/soft state. The revealed observational correlations allow us to propose a scenario for the spectral transition and iron line formation which occur in BHC sources. We also present the spectral state (the power-law index) evolution for eight years of Cyg X-1 observations by RXTE.

Shaposhnikov, Nickolai↗
NASA NTRS1985

Tunable diode laser mesurements of widths of air- and nitrogen-broadened lines in the nu(4) band of C-13H4

Tunable diode laser measurements of air-broadened and N2-broadened halfwidths are reported for 23 lines in the nu(4) band of C-13H4, between 1260 and 1360/cm. For all lines, at least three scans of each of four or more pressures were recorded. The experimental halfwidths presently obtained for C-13H4 are both larger and smaller than the U.S. Air Force Geophysics Laboratory values.

Devi, V. M.↗
NASA NTRS1979

Intensities and N2 collision-broadening coefficients measured for selected H2O absorption lines between 715 and 732 nm

Intensities and N2 collision-broadening coefficients are measured for 62 water vapor absorption lines between 715 and 732 nm potentially applicable to laser remote sensing of atmospheric water vapor. Absolute line strengths and widths were determined from spectra corrected for instrument resolution, air-path absorption and Lorentz and Doppler broadening for pure water vapor and water vapor-nitrogen mixtures in a multipass absorption cell with a base path length of 25 m (White cell). Line strengths are observed to range from 4 x 10 to the -25th to 4 x 10 to the -23rd kayser/molecule per sq cm, and collision broadening coefficients are found to be approximately equal to 0.1 kayser/atm.

Wilkerson, T. D.↗